An important technique to deliver video over the open Internet is HAS (HTTP (Hyper Text Transport Protocol) Adaptive Streaming). This technique has the advantage that it is easily deployable, because it traverses firewalls more easily than other protocols, because it has inherent congestion control which it inherits from TCP (Transport Control Protocol), and because it can make use of the existing HTTP infrastructure, in particular HTTP caches and CDN (Content Distribution Network) nodes.
According to the design principle of HAS, video is encoded at different bit rates and the client can switch between these bit rates at specified moments in time. Often the interval of video between two consecutive switching times is referred to as a video segment, while the bit strings associated with that interval are referred to as chunks (i.e., there are as many different chunks available as there are bit rate versions).
Today, there are no fully satisfactory mechanisms to select the most appropriate chunk relative to network performance.